1. Field of the Invention
The present invention relates to an internal-combustion-engine control apparatus that controls knocking caused by a pressure wave produced through self-ignition of an end gas in a cylinder of an internal combustion engine.
2. Description of the Related Art
When knocking occurs in an internal combustion engine (referred to as an engine, hereinafter), a vibration having a characteristic resonance frequency component occurs. Accordingly, by detecting the vibration, the occurrence of knocking can be determined. To date, an apparatus has been proposed (for example, Japanese Patent Publication No. 3471034) in which the AD-converted value of a knocking sensor signal outputted from a knocking sensor is divided every predetermined number in a plurality of frequency bandwidths and undergoes a fast Fourier transformation (referred to as an FFT, hereinafter) so that respective spectrums, in the frequency bandwidths, within a knocking detection window are calculated, the peak values in the respective spectrums in the frequency bandwidths are calculated, and then knocking control is performed based on the peak values.
Additionally, an apparatus has been proposed (for example, Japanese Patent Publication No. 3093467) in which the AD-converted value of a knocking sensor signal outputted from a knocking sensor is divided every predetermined number in a plurality of frequency bandwidths and undergoes an FFT, so that respective spectrums, in the frequency bandwidths, within a knocking detection window are calculated, the integration values of the spectrums in the frequency bandwidths are calculated, and then knocking control is performed based on the integration values.
FIGS. 4A to 4B are explanatory graphs for explaining the foregoing conventional apparatus; FIG. 4A represents the behavior of a knocking detection amount calculated based on the respective peak values in the frequency bandwidths; FIG. 4B represents the behavior of a knocking detection amount calculated based on the respective integration values in the frequency bandwidths; FIG. 4C represents the behavior of a knocking delay angle amount; FIG. 4D represents the behavior of an ignition timing after a knocking delay amount has been applied. A knocking detection amount NP represented in FIG. 4A is calculated as a value obtained by subtracting the peak value in the spectrum of the knocking sensor signal from a predetermined threshold value (in this regard however, in the case where the value obtained by subtracting a peak value in the spectrum of the knocking sensor signal from a predetermined threshold value becomes a negative value, the knocking detection amount NP is regarded as zero); a knocking detection amount NI represented in FIG. 4B is calculated as a value obtained by subtracting the integration value of the knocking sensor signal from a predetermined threshold value (in this regard however, in the case where the value obtained by subtracting an integration value of the knocking sensor signal from a predetermined threshold value becomes a negative value, the knocking detection amount NI is regarded as zero).
In the case where the knocking detection amount is larger than zero, the knocking delay angle amount is updated toward the delayed angle side (a side where the knocking delay angle amount increases) in proportion to the knocking detection amount; in the case of the knocking detection amount NP calculated based on the peak values of the respective spectrums in the frequency bandwidths, the behavior of the knocking delay angle amount is represented by the dashed line NPA in FIG. 4C; in contrast, in the case of the knocking detection amount NI calculated based on the integration values of the respective spectrums in the frequency bandwidths, the behavior of the knocking delay angle amount is represented by the broken line NIA in FIG. 4C. In other words, in the case where the knocking detection amount NP or NI is larger than zero, it is determined that there exists knocking, and the knocking delay angle amount increases.
In the case where the conventional technologies disclosed in Japanese Patent Publication No. 3471034 and Japanese Patent Publication No. 3093467 are utilized simply in combination with each other, i.e., in the case where the knocking detection amount NP and the knocking detection amount NI are utilized simply in combination with each other, the behavior of the knocking delay angle amount is represented by the solid line NPIA in FIG. 4C.
In the case where the knocking detection amount is zero, it is determined that there exists no knocking, and each time a knocking-free period exceeds predetermined duration, the knocking delay angle amount is updated toward the advanced angle side (a side where the knocking delay angle amount decreases). Additionally, as represented in the duration C in each of FIGS. 4A to 4C, the knocking detection amount NP calculated based on the peak value and the knocking delay angle amount NI calculated based on the integration value differ from each other in amplitude. The reason why the knocking detection amount NP and the knocking delay angle amount NI differ from each other in amplitude is that the values of the peak value and the integration value differ from each other and the respective predetermined threshold values differ from each other; as a result, as represented in FIG. 4C, the knocking delay angle amount NPA and the knocking delay angle amount NIA differ from each other in amplitude.
Here, close attention will be paid to the behaviors of the knocking delay angle amounts during the duration A and the duration B in FIG. 4C. In the first place, because, during the duration A, the knocking detection amount NI calculated based on the integration value is larger than zero, the knocking delay angle amount NIA calculated based on the integration value increases, and because the knocking detection amount NP calculated based on the peak value is zero, the knocking delay angle amount NPA calculated based on the peak value decreases. In this regard however, during the duration A, the knocking delay angle amount NPA calculated based on the peak value is larger than the knocking delay angle amount NIA calculated based on the integration value. During the duration A, it is determined based on the integration value that there exists knocking; therefore, it is required to increase the knocking delay angle amount so as to avoid the knocking.
However, in the case where the foregoing conventional technologies are utilized simply in combination with each other and knocking control is performed based on the knocking delay angle amount, out of the knocking delay angle amounts calculated in accordance with both conventional technologies, which is larger than the other, the knocking delay angle amount NPA calculated based on the peak value is selected, and the knocking delay angle amount NPIA decreases, even though it is determined during the duration A that there exists knocking; as a result, as represented in FIG. 4D, in the case where the conventional technologies are utilized simply in combination with each other, the ignition timing (after the knocking delay angle amount has been applied) is controlled toward the advanced angle side, even though it is determined during the duration A that there exists knocking.
In addition, in FIG. 4D, the curve TP represents the behavior of the ignition timing obtained after the knocking delay angle amount has been applied in the case where the foregoing conventional technologies are utilized simply in combination with each other; the curve TI represents the behavior of the ignition timing obtained after the knocking delay angle amount has been applied in the case where the present invention described later is utilized.
Because, during the duration B in FIG. 4C, the knocking detection amount NP calculated based on the peak value is larger than zero, the knocking delay angle amount NPA calculated based on the peak value increases, and because the knocking detection amount NI calculated based on the integration value is zero, the knocking delay angle amount NIA calculated based on the integration value decreases. In this regard however, during the duration B, the knocking delay angle amount NIA calculated based on the integration value is larger than the knocking delay angle amount NPA calculated based on the peak value. As described above, during the duration B, it is determined based on the peak value that there exists knocking; therefore, it is required to increase the knocking delay angle amount so as to avoid the knocking.
However, in the case where the conventional technologies are utilized simply in combination with each other and knocking control is performed based on the knocking delay angle amount, out of two knocking delay angle amounts calculated in accordance with both technologies, which is larger than the other, as represented in FIG. 4C, the knocking delay angle amount NIA calculated based on the integration value is selected, and during the duration B, the knocking delay angle amount NPIA decreases, even though it is determined that there exists knocking; as a result, as represented in FIG. 4D, in the case where the conventional technologies are utilized simply in combination with each other, as is the case with the duration A, the ignition timing TP obtained after the knocking delay angle amount has been applied is controlled toward the advanced angle side, even though it is determined that there exists knocking. As described above, in the case where the foregoing conventional technologies are utilized simply in combination with each other, appropriate knocking control may not be performed.
As well known by those skilled in the art, depending on the shape of an engine block, the shape of a cylinder, the opening/closing timings of an air-intake valve and an exhaust gas valve, the difference in an fuel injection system, and the like, a vibration due to knocking and vibrations due to various kinds of noise signals change; thus, as disclosed in Japanese Patent Publication No. 3471034, there exists an engine in which knocking detectability is enhanced by performing knocking control on the basis of the peak values of the spectrums in the frequency bandwidths, or as disclosed in Japanese Patent Publication No. 3093467, there exists an engine in which knocking detectability is enhanced by performing knocking control on the basis of the integration values of the spectrums in the frequency bandwidths.
Moreover, even in the same engine, depending on a driving condition, knocking detectability is enhanced by performing knocking control on the basis of the peak values of the spectrums in the frequency bandwidths, or knocking detectability is enhanced by performing knocking control on the basis of the integration values of the spectrums in the frequency bandwidths. In other words, with such conventional technologies as disclosed in Japanese Patent Publications No. 3471034 and No. 3093467, an engine with low knocking detectability may be manufactured or a driving condition in which knocking detectability is low may occur.
Still moreover, in the case where such a conventional technology as disclosed in Japanese Patent Publication No. 3471034 and such a conventional technology as disclosed in Japanese Patent Publication No. 3093467 are utilized simply in combination with each other and knocking control is performed on the basis of the knocking delay angle amount (i.e., the amount of an angle by which the ignition timing is delayed in order to avoid knocking), out of the knocking delay angle amounts calculated in accordance with both technologies, which is larger than the other, the knocking delay angle amount calculated based on the integration value is selected in a certain duration, and the knocking delay angle amount decreases, even though it is determined that there exists knocking; thus, the ignition timing obtained after the knocking delay angle amount has been applied is controlled toward the advanced angle side, whereby appropriate knocking control may not be performed.